The present invention relates generally to sensors particularly suited for automotive vehicles, and more particularly, to a circuit for interfacing with a sensor.
Automotive vehicles typically provide a number of sensors that are used to sense various operating conditions of the vehicle. Systems that are sensor intensive include vehicle handling systems such as anti-lock brakes and traction control, and safety systems such as airbag systems.
Sensor based systems typically use a microcontroller to read multiple asynchronous remote sensor signals with serial state machines. Serial state machines such as a universal asynchronous receive transmitter (UART) are typically employed as an interface device. Typically, two UARTs are provided per sensor; one in the controller as well as one UART at each remote sensor. However, many systems have multiple sensors and therefore require multiple UARTs.
Previous systems use a digital word to transmit data between the sensor and central controller. The digital word corresponds to the sensed condition at the sensor. The digital word operates only when the sensor is to send a signal. Previous systems often generate noise emissions due to the sharp on and off transitions of the digital communication signal.
It would therefore be desirable to provide an interface for receiving signals from a remote sensor that, when implemented, uses a reduced number of components from presently known systems synchronizes remote sensor data acquisition using readily available hardware.
In one aspect of the invention, a circuit has a sensor having a sensor and a modulated sensor current signal corresponding to a sensed condition. A control module is coupled to the sensor and receives the sensor current signal. The control module converts the sensor current signal to a pulse width with a duration corresponding to the sensed condition. The control module measures a time corresponding to the pulse width. The time corresponds to the sensed condition.
In a further aspect of the invention, a method for communicating a sensed condition of a sensor comprises the steps of:
modulating a sensor current signal corresponding to a sensed condition;
generating a pulse width corresponding to the sensor current signal;
monitoring a time corresponding to said pulse width; and
converting the time into a digital value, wherein the time corresponds to a sensed condition.
One advantage of the invention is that a current modulated signal from the sensor circuit to the central controller has reduced electromagnetic interference than previously known sensing circuits due to the ability of use of a substantially triangular signal with rounded transitions rather than sharp transitions. Another advantage of the invention is that drift in the remote sensor""s quiescent current due to age, temperature and tolerances are tracked by the voltage comparator which uses the average current for comparison.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.